1. Field of the Invention
The present invention concerns a method of fabricating Si nanocrystals. In particular, it relates to Si nanostructures which are useful in applications such as, semiconductor quantum dots, nonlinear optical devices, and quantum wave interference materials, as well as to a method of manufacturing such nanocrystalline structures.
2. Description of the Related Art
Prior methods of fabricating semiconductor superlattice structures involve application of vacuum evaporation using MBE or CVD to prepare a one-layered structure, or application of lithography and etching technology to prepare two-dimensional or three-dimensional structures. However, in the former method, positional control of its arrangement is difficult, and in recent years, a method to vacuum evaporate fine particles at random and then forming a regular arrangement on the substrate through a self-restoration process has been considered. Yet, this method has not yet been established as a practical technique. On the other hand, the latter method allows positional control, but can only provide structures of which the minimum size is in the order of ten nm, while finer structures are demanded.
For some years, in order to apply lithography/etching technology in fabricating finer structures, the use of focused electron beam has been considered.
For example, decomposition of SiO2 by irradiating focused electron beam to precipitate Si on its surface, has been known as the electron-stimulated desorption mechanism (ESD) (M. L. Knotek and P. J. Feibelman, Surf. Sci., 90, 78 (1979)). Also, in recent years, a study has been reported on preparing amorphous Si particles 2 nm in size by ESD at room temperature, utilizing focused electron beam from a field emission electron microscope, and arranging them on amorphous SiO2 with positional control (G. S. Chen, C. B. Boothroyd and C. J. Humphreys, Appl. Phys. Lett., 62, 1949 (1993)). However, no detailed studies have been made on the formation of Si nanocrystals by ESD, and the Si that had been manufactured in the latter study was, actually, merely of an amorphous structure. The quantum size effect in a superlattice is remarkable in crystals but small in the amorphous state, because the band structure of amorphous particles does not depend on size, unlike in crystalline materials, and quantum size effect can not be expected.
In view of the above situation, the present invention has been invented as a result of intensive study, and its main object is to provide a novel method which allows the formation of single crystalline Si nanostructures by the irradiation of electron beams, which also allows excellent size and position controllability.
Another object of the present invention is to provide Si nanostructures not known so far, obtained by using the method described above.